DE 10 2006 011 713 A1 discloses a generic electronic overcurrent release for motor circuit breakers. For each of the current phases which are to be switched and protected, the overcurrent release comprises the primary side of a current transformer, the secondary side of which is connected to a load resistor via a rectifier arrangement. When the current transformers are unsaturated, the load voltages are a proportional function of the phase currents. Via smoothing circuits, the load voltages reach a microcontroller. The outputs of two multi-stage setting switches are also located at the microcontroller. A suitable nominal current value for the load which is connected to the circuit breaker can be selected by means of the first setting switch. By means of the second setting switch, the lag level for the release of the circuit breaker is selected, that is to say the delay with which a load which is connected to the circuit breaker is to be switched off if at least one of the phase currents persistently exceeds the selected nominal current. The greater the amount by which the set nominal current value is exceeded, the more rapidly the load is switched off. As a function of the selected settings, a corresponding overcurrent release characteristic is activated in the microcontroller. When an overcurrent occurs, that is to say as a result of the set nominal current value being exceeded for a delay time which corresponds to the selected lag level and to the measured overcurrent, a release signal is emitted at the output of the microcontroller, and after amplification is supplied to an electromagnetic actuator, which in turn releases the switch mechanism of the circuit breaker to switch off. For overcurrents of the short circuit type, a signal is supplied to the microcontroller via a threshold circuit by way of the corresponding load voltage, and this causes rapid release. Moreover, the voltage for the active electronic components of the release unit is supplied from the output of the rectifier circuits.
DE 102 09 068 C1 discloses a testing arrangement for electronic overcurrent releases of this type of a circuit breaker. The testing arrangement comprises a testing unit, which corresponds to the circuit breaker, which is calibrated to and tested for current values, and which is also loaded by the circuit breaker by way of the test variable. Further, a monitoring unit is provided for detecting and signalling the release of the overcurrent release. For this purpose, the load has to be separated from the circuit breaker, and the feed and load terminals of all of the phase currents of the circuit breaker have to be connected in series and be loaded by a test current source. Further, the secondary sides of the current transformers, which are now loaded by the same test current, of the overcurrent release have to be separated in part from the evaluating components of the overcurrent release and instead connected to the testing unit of the test arrangement. For this purpose it can be tested, at the place of use of the circuit breaker, whether the chain of action for the electronic release works and the release takes place within the acceptable tolerances.
Often, a prediction is merely required as to whether, at the place of use of a circuit breaker, the electronic overcurrent release will work over the entire chain of action, without making quantitative predictions as to the adherence to tolerance limits, at a considerable expense in terms of testing means, load disconnection and series connection of the phase terminals of the circuit breaker, as well as bypasses for the current transformer outputs.